The fast solution is simple and not pleasing… but papermatching WORKS.
http://www.woodhavenlabs.com/tplo-normal.html
Take a paper match and wet the head of the match in your mouth for a few seconds. Then take the match and insert the head end first into the dog's rectum. Make sure part of the match is hanging out. Within a few seconds the dog should start to get into the position to poop and be successful at doing so. (I had to do this for Darby for about 2-3 weeks)<<
So you papermatch and praise like crazy.
As for tying him out, most can chew through MOST lines so I would be careful. Better to papermatch til he will go on command in your own yard.
Also, how secure is your yard? Can you put him out while you are getting son ready for school alone? However, getting up a bit early to MAKE him potty, THEN secure him (get clips on cage so he cannot escape!) in crate while you take child to school, is better.
Btw, 2 wks is a short time, it will all come together!
Debra